1. Field of the Invention
The present invention relates to input polarization-induced phase noise in interferometric fiber-optic sensors and particularly to a system and method for minimizing such polarization-induced noise in an interferometric fiber-optic sensor by scrambling the state of polarization of the light input to the interferometer in such a sensor.
2. Description of the Prior Art
In recent years interferometric fiber-optic sensors have been configured to detect a wide range of physical fields, such as acoustic waves and temperature fluctuations. These sensors typically operate with high sensitivity, good linearity, and over a wide dynamic range.
In operation, an interferometric fiber-optic sensor combines the light beams from two optical paths (through signal and reference arms) in the interferometer of the sensor and causes them to interfere to produce an interference pattern that is proportional to the field being sensed by the sensor. Fluctuations in the polarization state of the input light to the sensor can lead to the generation of phase noise in the output interference signal of the sensor.
It is commonly assumed that interferometric fiber sensors are "lead insensitive", or that perturbations of the input fiber to an interferometer or to the output fiber from that interferometer do not give rise to a shift in the phase of the interference signal generated at the associated detector. However, it can be shown that fluctuations in the input state of polarization (SOP) to an interferometric sensor can result in the generation of phase noise in the demodulated output of the interferometric fiber sensor.